The Battle of Gettysburg Cyclorama painting at Gettysburg National Military Park Museum is being given a special clean by chief conservator David L. Olin and visitors are able to watch the process while hearing a narrative of the scenes in the painting, via a sound & light programme.

For those readers who are unfamiliar with this incredible oil painting, it was created in the late 1880s by French artist Paul Philippoteaux and a team of assistants, following months on the battlefield researching the Battle of Gettysburg with veterans, a battlefield guide and a photographer. It took more than a year to complete. Quite a feat perhaps when one considers that it measures 377 feet in circumference, is 42 feet high and weighs some 12.5 tons. That makes it longer than a football field and as tall as a four-storey structure.

Over the years, the painting has survived fire, leaks, tears, rotting, temperature and humidity fluctuations. To accommodate exhibit spaces over time, it has been sliced into panels and approximately 15 feet of the sky part of it has been removed over the years. All this took a toll on the painting, creating seams and bends and causing chips in the paint. By the late 1990s, experts warned that unless it was repaired it could be lost forever.

Repairing the painting has required painstaking work by art conservationists under the direction of David Olin, Olin Conservation, Great Falls, Va. Experts repaired unstable sections of the canvas and restored details lost during previous conservation attempts in what has been described as the biggest conservation project ever carried out in North America.

Each year David Olin assesses the condition of the painting and his most recent assessment - after three years of display - showed some surface grime, particularly along the upper portion of the canvas, as well as some grime and dust accumulating on the reverse of the canvas lining. This now has to be tackled and visitors attending during the week (but not at weekends) can see how it's done.